TECHNOLOGY; I.B.M. Computer Researchers Push Tiny to a New Extreme

I.B.M. scientists have for the first time created a vast assembly of transistors using a new material only a few molecules wide, taking a significant step toward computers far tinier and more powerful than those used today.

The advance, which is to be reported Friday in Science magazine, is the first case of researchers' having successfully harnessed this material for electronics, holding out promise for a future electronics industry based on components perhaps one five-hundredth the width of the silicon transistors that power computers today.

The hunt for advanced electronic materials is driven in part by the physical limits of the current silicon chip. The number of transistors that can be placed on a chip has doubled about every 18 months for more than three decades. But a point could soon be reached where the wires needed to connect them would have to be finer than current materials and manufacturing allow.

The I.B.M. researchers were cautious about near-term commercial applications of their technology, which is based on ultrafine threads known as carbon nanotubes. But the research comes at a time when rapid progress is being reported by both corporate and academic researchers who are pressing advances in a novel field known as molecular electronics.

A number of start-up companies have been founded in the last two years specifically to explore ultratiny electronic devices built with technologies beyond those now used in the semiconductor industry. The hope is to create sophisticated electronics that pack far more computing force in smaller devices, while consuming less electrical power and producing less heat.

''All of the brains are lined up thinking about a new kind of electronics based on nanotechnology,'' said Richard E. Smalley, the Rice University chemist who shared the Nobel Prize in 1996 for the invention of buckyballs, a similar carbon-based molecule.

Dr. Smalley was one of 85 scientists who attended a conference this week on challenges facing nanotechnology -- technology based on the tiniest molecular structures -- at I.B.M.'s Almaden Research Center in San Jose, Calif., in the foothills south of Silicon Valley.

Nanotubes are structures only a handful of atoms across that form spontaneously from hexagonal arrays of carbon atoms. They were discovered in 1991 by Dr. Sumio Iijima of the NEC Fundamental Research Laboratories in Tsukuba, Japan. The tubes, actually elongated molecules, form in furnaces from vapor generated by carbon arcs and lasers. They take their name from the nanometer, a unit of measurement one-billionth of a meter long -- a convenient length for specifying molecular dimensions.

The ultrathin filaments have long fascinated scientists, but until now they have been maddeningly difficult to work with, because they tend to clump together in a messy interwoven form akin to steel wool.

Some of the tiny fibers can alternately conduct electricity or insulate, a basic quality of semiconducting materials. That quality has led scientists to speculate that in the future carbon nanotubes might become the basic wire and switching material for a generation of computers in which components are no more than a handful of molecules in size.

The three scientists at the I.B.M. laboratory in Yorktown Heights, N.Y., took a step in that direction by succeeding in building tiny electronic switches made with thin carbon nanotube wires.

The Lilliputian size of the nanotube wires is breathtaking, on the average only about 1.4 nanometers in diameter, or about the width of 10 atoms. In contrast, the same component in today's transistors is about 500 nanometers in width.

Some of the tiny tubes have metallic, electrically conductive properties, while others are semiconducting. Moreover, some of the carbon nanotubes have a single wall, like a pipe made from a tiny matrix of carbon atoms, while others are composed of many concentric shells that may be either metallic or semiconducting.

By applying a thin slurry of carbon nanotubes on top of a conventional silicon chip, the I.B.M. scientists, Philip G. Collins, Michael S. Arnold and Phaedon Avouris, were able to drape tiny bundles of nanotubes across conventional metallic contacts and then remove the metallic nanotubes by applying a current, effectively vaporizing the metallic wires or shells and leaving only a semiconducting nanotube in place. Dr. Avouris referred to the process as ''constructive destruction.''

Additionally, the I.B.M. researchers said they thought they would ultimately be able to precisely tailor the length of the carbon nanotubes. The channel length, or the spacing between the source and the drain of a modern transistor, is a critical factor determining the switching speed of the devices and thus the speed of the computers they enable. Ultrashort carbon nanotubes could create machines that would reach fantastic speeds, the scientists said.

Individual transistors using carbon nanotubes were first created in 1998 by several research groups, but this is the first time it has been shown that it is possible to repeat the process in a precise and controlled fashion.

''On a practical level, this controlled destruction allows us to effectively separate semiconducting single-wall nanotubes from mixtures of single-wall nanotubes and easily generate nanotube field effect transistors,'' the scientists wrote in the Science paper.

The results were greeted by many scientists in the field as dramatic because Dr. Avouris, who has a reputation as one of the most exacting scientists in the field of device physics, has also been widely known as a skeptic about many of the claims made recently by other researchers in the emerging field of molecular electronics.

''He's a very careful experimentalist, and he's lived at the center of efforts to make many improvements in computer technology and has seen some things fail,'' said Dr. James C. Ellenbogen, a chemical physicist at the Mitre Corporation.

In an interview this week at the I.B.M. Almaden laboratory, Dr. Avouris said he remained skeptical about many of the radical ideas being pursued by other researchers that employ organic molecules as electronic switches. Frequently those devices either switch very slowly or without the precision of today's silicon transistors, he said.

He said, though, that he now thought that at some point in the future a hybrid electronics blending carbon nanotubes and silicon might be a reality.

''I don't expect that nanotubes will make it as an independent technology,'' he said, ''however, in principle we now have the potential for forming an integrated electronics.''

Other scientists said that the I.B.M. advance was a remarkable achievement. They noted that the conservatism of Dr. Avouris was not universally shared by many of the researchers in the field who are now looking for ways around the limits of silicon technology.

''People who know a lot about the electronics industry will tend to be very conservative,'' said Dr. Alex Zettl, a professor of physics at the University of California at Berkeley, who is an expert in carbon nanotubes. ''On the other hand, new ideas push technologies forward, and without these ideas we'd still be sharpening our stone axes.''